Printing processes, such as liquid electro-photographic (LEP) printing and transfer printing, may result in ink waste or leftover ink. For example, ink waste or leftover ink may be generated when ink fountains are cleaned, when ink has exceeded its shelf life, or when ink has been contaminated. Ink waste or leftover ink may be difficult to dispose of and may include an oil-based carrier, such as solvents sold under the Exxon Mobil Corporation trademarked name ISOPAR™, colorants, polar and protic additives, and other impurities.
The carrier in ink waste can be recycled if it is filtered of colorants, polar and protic additives, and other impurities, such that the remaining filtered carrier has a conductivity less than 10 pico-Siemens per centimeter (pS/cm) and no absorbance when it is exposed to light having wavelengths between 380 nanometers (nm) and 800 nm. Using ink with recycled carrier that has absorbance at any wavelength between 380 nm and 800 nm or has a conductivity greater than 10 pS/cm indicates the presence of residual impurities which may result in undesirable disturbances to the jetting performance and stability of the printing process.